Medical injection devices are used to deliver selected doses of medication to patients. Some medication, such as insulin is self-administered. The typical diabetes patient will require injections of insulin several times during the course of the day. In order to prevent infections it is recommended to use a sterile needle assembly for each injection. Needle assemblies are often delivered in magazines where each magazine contains only one needle assembly in a sterile compartment. Such a magazine is described in U.S. Pat. No. 5,971,966. Using a needle assembly of this kind requires the patient to open the magazine and to fasten the needle assembly on to the injection device prior to each injection. The storage of sterile needle assemblies of this type and the final disposal of used needle assemblies present a problem since new sterile needle assemblies are often carried loosely in purses or briefcases. Furthermore, used needle assemblies are often disposed of unsafely.
To overcome these problems a needle magazine for storing and dispensing a plurality of needle assemblies has been proposed in U.S. Pat. No. 5,829,589. The needle magazine is provided as a container having a plurality of cavities each accommodating a needle assembly. A cover is rotatably mounted on top of the container. When aligning a slot in the cover with one of the cavities, the user can access the cavity. The needle assembly is connected to the injection device by forcing the tip of the injection device into the cavity where the needle assembly is force fitted, e.g. by a well-known luer-coupling, onto the tip of the injection device. The needle assembly can then be detached from the magazine. When the used needle is to be returned to the magazine the user has to conduct a reverse procedure.
The above prior art needle magazine is attached to the injection device by fitting the entire magazine into an open end of the removable cap of a pencil-shaped injection device. Due to the dimensions of a pencil-shaped injection device only five needle assemblies can be contained in the magazine. An ordinary disposable injection device usually contains 300 IU of insulin. For many diabetes patients this is sufficient for 10 to 20 injections, therefore one magazine of needle assemblies are not enough for the lifetime of one disposable injection device, which is very inconvenient.
US 2002/0020646 discloses another needle magazine which is intended to be mounted onto the dispensing portion (the distal end) of an injection device. The needle magazine includes a rotatable cassette holding a plurality of needles in a circular array configuration. By sequentially rotating the cassette, each of the needles can be brought into alignment with the distal end of the injection device. By moving the injection device in the distal direction, the back needle of the particular selected needle penetrates a septum in the cartridge. Further distal movement causes the front needle to penetrate a seal in a distal face of the needle container to bring the selected needle into an injection position.
Even though the needle magazine according to US 2002/0020646 may include a large number of needles, this needle magazine is rather bulky and takes up much space in the plane which includes the array. If the needle magazine is dimensioned to hold several needles, the circular array extends quite far in a direction transverse to the needle which is aligned with the cartridge, particular in the direction which intersects the centre axis of the circular array. Thus, the geometric form of the needle magazine according to US 2002/0020646 is practically not adaptable to all kinds of injection devices, in particular not to injection devices of the pen-shaped form factor.